The present invention relates generally to implantable medical leads and more specifically to pacemaker and defibrillation leads employing stranded conductors.
Traditionally, implantable cardiac pacing and defibrillation leads have employed monofilar or multifilar coiled conductors, as illustrated in U.S. Pat. No. 4,355,646 issued to Kallok et al. More recently, cabled or stranded conductors have gained wider acceptance, for example, as disclosed in U.S. Pat. No. 5,584,873 issued to Shoberg et al. and incorporated herein by reference in its entirety and U.S. Pat. No. 5,760,341 issued to Laske et al., also incorporated herein by reference in its entirety. In conjunction with the use of stranded conductors, new mechanisms for interconnecting the conductors to other electrically conductive lead components have had to be developed. One such mechanism for coupling stranded conductors to electrical components in a lead is a press-fit sleeve, as disclosed in U.S. patent application Ser. No. 08/439,332 for a "Medical Lead With Stranded Conductors", filed May 11, 1995 by Swoyer et al, also incorporated herein by reference in its entirety.
In the particular context of defibrillation leads, use of the electrodes on the leads to sense electrical signals in a bipolar fashion has typically been accomplished by one of two ways. The first mechanism for accomplishing bipolar sensing is to simply provide a tip electrode and a ring electrode, as commonly used in bipolar cardiac pacing leads, for example as illustrated in U.S. Pat. No. 4,614,192 issued to Imran et al. Alternatively, bipolar sensing can be provided by means of what has come to be known as an "integrated bipolar" system, wherein one of the defibrillation electrodes on the lead also serves as a sensing electrode, in conjunction with the distal or tip electrode on the lead. A lead employing an integrated bipolar electrode system is disclosed in U.S. Pat. No. 4,603,705 issued to Speicher et al. In such a lead, it is necessary to couple the defibrillation electrode which also serves as the sensing electrode to separate electrical connectors, so that it may be coupled to the input terminal of the sense amplifier on an associated implantable cardioverter/defibrillator and to the cardioversion/defibrillation output terminal.
While the lead illustrated in the Speicher patent employs separate connector pins for each connection to the pulse generator, it has become more common to connect sensing electrodes using a bipolar in-line connector conforming to the IS-1 connector standard, typically employed on leads intended for use with implantable pacemakers, as disclosed in U.S. Pat. No. 5,476,501 issued to Stewart et al., incorporated herein by reference in its entirety. In the context of a lead which employs an advanceable fixation helix located at its distal end, it is conventional to employ a coiled conductor, rotatable within the lead body and coupled to a rotatable connector pin extending from the proximal end of the connector assembly as the mechanism for rotating the fixation helix, as also disclosed in U.S. Pat. No. 5,476,501 issued to Stewart et al.